Add base85, based on base64.

Also add git version of base85,
which is what I really wanted but
didn't recognize as different until it
was too late.

R=austin
DELTA=980  (972 added, 4 deleted, 4 changed)
OCL=35580
CL=35921

8 files changed, 976 insertions, 8 deletions

diff --git a/src/pkg/Make.deps b/src/pkg/Make.deps
index 9d091ea96..1114f5515 100644
--- a/src/pkg/Make.deps
+++ b/src/pkg/Make.deps
@@ -1,6 +1,7 @@
 archive/tar.install: bytes.install io.install os.install strconv.install strings.install
 asn1.install: fmt.install os.install reflect.install strconv.install strings.install time.install
 base64.install: bytes.install io.install os.install strconv.install
+base85.install: bytes.install io.install os.install strconv.install
 big.install:
 bignum.install: fmt.install
 bufio.install: io.install os.install strconv.install utf8.install
diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index bbc4536de..8761558de 100644
--- a/src/pkg/Makefile
+++ b/src/pkg/Makefile
@@ -15,6 +15,7 @@ DIRS=\
 	archive/tar\
 	asn1\
 	base64\
+	base85\
 	big\
 	bignum\
 	bufio\
diff --git a/src/pkg/base64/base64.go b/src/pkg/base64/base64.go
index 111dc1da6..b4daee3cc 100644
--- a/src/pkg/base64/base64.go
+++ b/src/pkg/base64/base64.go
@@ -16,7 +16,7 @@ import (
  * Encodings
  */
 
-// Encoding is a radix 64 encoding/decoding scheme, defined by a
+// An Encoding is a radix 64 encoding/decoding scheme, defined by a
 // 64-character alphabet.  The most common encoding is the "base64"
 // encoding defined in RFC 4648 and used in MIME (RFC 2045) and PEM
 // (RFC 1421).  RFC 4648 also defines an alternate encoding, which is
@@ -56,7 +56,7 @@ var URLEncoding = NewEncoding(encodeURL)
  */
 
 // Encode encodes src using the encoding enc, writing
-// EncodedLen(len(input)) bytes to dst.
+// EncodedLen(len(src)) bytes to dst.
 //
 // The encoding pads the output to a multiple of 4 bytes,
 // so Encode is not appropriate for use on individual blocks
@@ -134,7 +134,6 @@ func (e *encoder) Write(p []byte) (n int, err os.Error) {
 			return;
 		}
 		e.enc.Encode(&e.buf, &e.out);
-		var _ int;
 		if _, e.err = e.w.Write(e.out[0:4]); e.err != nil {
 			return n, e.err;
 		}
@@ -142,7 +141,7 @@ func (e *encoder) Write(p []byte) (n int, err os.Error) {
 	}
 
 	// Large interior chunks.
-	for len(p) > 3 {
+	for len(p) >= 3 {
 		nn := len(e.out)/4*3;
 		if nn > len(p) {
 			nn = len(p);
@@ -150,7 +149,6 @@ func (e *encoder) Write(p []byte) (n int, err os.Error) {
 		nn -= nn%3;
 		if nn > 0 {
 			e.enc.Encode(p[0:nn], &e.out);
-			var _ int;
 			if _, e.err = e.w.Write(e.out[0 : nn/3*4]); e.err != nil {
 				return n, e.err;
 			}
@@ -175,7 +173,6 @@ func (e *encoder) Close() os.Error {
 	if e.err == nil && e.nbuf > 0 {
 		e.enc.Encode(e.buf[0 : e.nbuf], &e.out);
 		e.nbuf = 0;
-		var _ int;
 		_, e.err = e.w.Write(e.out[0:4]);
 	}
 	return e.err;
@@ -206,7 +203,7 @@ func (e CorruptInputError) String() string {
 	return "illegal base64 data at input byte" + strconv.Itoa64(int64(e));
 }
 
-// decode is like Decode, but returns an additional 'end' value, which
+// decode is like Decode but returns an additional 'end' value, which
 // indicates if end-of-message padding was encountered and thus any
 // additional data is an error.  decode also assumes len(src)%4==0,
 // since it is meant for internal use.
@@ -262,7 +259,6 @@ func (enc *Encoding) Decode(src, dst []byte) (n int, err os.Error) {
 		return 0, CorruptInputError(len(src)/4*4);
 	}
 
-	var _ bool;
 	n, _, err = enc.decode(src, dst);
 	return;
 }
diff --git a/src/pkg/base85/Makefile b/src/pkg/base85/Makefile
new file mode 100644
index 000000000..2dae5b124
--- /dev/null
+++ b/src/pkg/base85/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include $(GOROOT)/src/Make.$(GOARCH)
+
+TARG=base85
+GOFILES=\
+	base85.go\
+	git.go\
+
+include $(GOROOT)/src/Make.pkg
diff --git a/src/pkg/base85/base85.go b/src/pkg/base85/base85.go
new file mode 100644
index 000000000..b8d250a17
--- /dev/null
+++ b/src/pkg/base85/base85.go
@@ -0,0 +1,307 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package base85 implements radix 85 encoding/decoding.
+package base85
+
+import (
+	"bytes";
+	"io";
+	"os";
+	"strconv";
+)
+
+/*
+ * Encoder
+ */
+
+// Encode encodes src into at most MaxEncodedLen(len(src))
+// bytes of dst, returning the actual number of bytes written.
+// Encode implements the ascii85 encoding as used in the btoa
+// tool and Adobe's PostScript and PDF document formats.
+//
+// The encoding handles 4-byte chunks, using a special encoding
+// for the last fragment, so Encode is not appropriate for use on
+// individual blocks of a large data stream.  Use NewEncoder() instead.
+func Encode(src, dst []byte) int {
+	if len(src) == 0 {
+		return 0;
+	}
+
+	n := 0;
+	for len(src) > 0 {
+		dst[0] = 0;
+		dst[1] = 0;
+		dst[2] = 0;
+		dst[3] = 0;
+		dst[4] = 0;
+
+		// Unpack 4 bytes into uint32 to repack into base 85 5-byte.
+		var v uint32;
+		switch len(src) {
+		default:
+			v |= uint32(src[3]);
+			fallthrough;
+		case 3:
+			v |= uint32(src[2])<<8;
+			fallthrough;
+		case 2:
+			v |= uint32(src[1])<<16;
+			fallthrough;
+		case 1:
+			v |= uint32(src[0])<<24;
+		}
+
+		// Special case: zero (!!!!!) shortens to z.
+		if v == 0 && len(src) >= 4 {
+			dst[0] = 'z';
+			dst = dst[1:len(dst)];
+			n++;
+			continue;
+		}
+
+		// Otherwise, 5 base 85 digits starting at !.
+		for i := 4; i >= 0; i-- {
+			dst[i] = '!' + byte(v%85);
+			v /= 85;
+		}
+
+		// If src was short, discard the low destination bytes.
+		m := 5;
+		if len(src) < 4 {
+			m -= 4 - len(src);
+			src = nil;
+		} else {
+			src = src[4:len(src)];
+		}
+		dst = dst[m:len(dst)];
+		n += m;
+	}
+	return n;
+}
+
+// MaxEncodedLen returns the maximum length of an encoding of n source bytes.
+func MaxEncodedLen(n int) int {
+	return (n+3)/4*5;
+}
+
+// NewEncoder returns a new ascii85 stream encoder.  Data written to
+// the returned writer will be encoded and then written to w.
+// Ascii85 encodings operate in 32-bit blocks; when finished
+// writing, the caller must Close the returned encoder to flush any
+// trailing partial block.
+func NewEncoder(w io.Writer) io.WriteCloser {
+	return &encoder{w: w};
+}
+
+type encoder struct {
+	err	os.Error;
+	w	io.Writer;
+	buf	[4]byte;	// buffered data waiting to be encoded
+	nbuf	int;		// number of bytes in buf
+	out	[1024]byte;	// output buffer
+}
+
+func (e *encoder) Write(p []byte) (n int, err os.Error) {
+	if e.err != nil {
+		return 0, e.err;
+	}
+
+	// Leading fringe.
+	if e.nbuf > 0 {
+		var i int;
+		for i = 0; i < len(p) && e.nbuf < 4; i++ {
+			e.buf[e.nbuf] = p[i];
+			e.nbuf++;
+		}
+		n += i;
+		p = p[i:len(p)];
+		if e.nbuf < 4 {
+			return;
+		}
+		nout := Encode(&e.buf, &e.out);
+		var _ int;
+		if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
+			return n, e.err;
+		}
+		e.nbuf = 0;
+	}
+
+	// Large interior chunks.
+	for len(p) >= 4 {
+		nn := len(e.out)/5*4;
+		if nn > len(p) {
+			nn = len(p);
+		}
+		nn -= nn%4;
+		if nn > 0 {
+			nout := Encode(p[0:nn], &e.out);
+			var _ int;
+			if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
+				return n, e.err;
+			}
+		}
+		n += nn;
+		p = p[nn:len(p)];
+	}
+
+	// Trailing fringe.
+	for i := 0; i < len(p); i++ {
+		e.buf[i] = p[i];
+	}
+	e.nbuf = len(p);
+	n += len(p);
+	return;
+}
+
+// Close flushes any pending output from the encoder.
+// It is an error to call Write after calling Close.
+func (e *encoder) Close() os.Error {
+	// If there's anything left in the buffer, flush it out
+	if e.err == nil && e.nbuf > 0 {
+		nout := Encode(e.buf[0:e.nbuf], &e.out);
+		e.nbuf = 0;
+		var _ int;
+		_, e.err = e.w.Write(e.out[0:nout]);
+	}
+	return e.err;
+}
+
+/*
+ * Decoder
+ */
+
+type CorruptInputError int64
+
+func (e CorruptInputError) String() string {
+	return "illegal ascii85 data at input byte" + strconv.Itoa64(int64(e));
+}
+
+// Decode decodes src into dst, returning both the number
+// of bytes consumed from src and the number written to dst.
+// If src contains invalid ascii85 data, Decode will return the
+// number of bytes successfully written and a CorruptInputError.
+// Decode ignores space and control characters in src.
+//
+// If flush is true, Decode assumes that src represents the
+// end of the input stream and processes it completely rather
+// than wait for the completion of another 32-bit block.
+//
+// NewDecoder wraps an io.Reader interface around Decode.
+//
+func Decode(src, dst []byte, flush bool) (nsrc, ndst int, err os.Error) {
+	var v uint32;
+	var nb int;
+	for i, b := range src {
+		if len(dst) - ndst < 4 {
+			return;
+		}
+		switch {
+		case b <= ' ':
+			continue;
+		case b == 'z' && nb == 0:
+			nb = 5;
+			v = 0;
+		case '!' <= b && b <= 'u':
+			v = v*85 + uint32(b - '!');
+			nb++;
+		default:
+			return 0, 0, CorruptInputError(i);
+		}
+		if nb == 5 {
+			nsrc = i+1;
+			dst[ndst] = byte(v>>24);
+			dst[ndst+1] = byte(v>>16);
+			dst[ndst+2] = byte(v>>8);
+			dst[ndst+3] = byte(v);
+			ndst += 4;
+			nb = 0;
+			v = 0;
+		}
+	}
+	if flush {
+		nsrc = len(src);
+		if nb > 0 {
+			// The number of output bytes in the last fragment
+			// is the number of leftover input bytes - 1:
+			// the extra byte provides enough bits to cover
+			// the inefficiency of the encoding for the block.
+			if nb == 1 {
+				return 0, 0, CorruptInputError(len(src));
+			}
+			for i := nb; i < 5; i++ {
+				// The short encoding truncated the output value.
+				// We have to assume the worst case values (digit 84)
+				// in order to ensure that the top bits are correct.
+				v = v*85 + 84;
+			}
+			for i := 0; i < nb-1; i++ {
+				dst[ndst] = byte(v>>24);
+				v <<= 8;
+				ndst++;
+			}
+		}
+	}
+	return;
+}
+
+// NewDecoder constructs a new ascii85 stream decoder.
+func NewDecoder(r io.Reader) io.Reader {
+	return &decoder{r: r};
+}
+
+type decoder struct {
+	err	os.Error;
+	readErr	os.Error;
+	r	io.Reader;
+	end	bool;		// saw end of message
+	buf	[1024]byte;	// leftover input
+	nbuf	int;
+	out	[]byte;	// leftover decoded output
+	outbuf	[1024]byte;
+}
+
+func (d *decoder) Read(p []byte) (n int, err os.Error) {
+	if len(p) == 0 {
+		return 0, nil;
+	}
+	if d.err != nil {
+		return 0, d.err;
+	}
+
+	for {
+		// Copy leftover output from last decode.
+		if len(d.out) > 0 {
+			n = bytes.Copy(p, d.out);
+			d.out = d.out[n:len(d.out)];
+			return;
+		}
+
+		// Decode leftover input from last read.
+		var nn, nsrc, ndst int;
+		if d.nbuf > 0 {
+			nsrc, ndst, d.err = Decode(d.buf[0:d.nbuf], &d.outbuf, d.readErr != nil);
+			if ndst > 0 {
+				d.out = d.outbuf[0:ndst];
+				d.nbuf = bytes.Copy(&d.buf, d.buf[nsrc:d.nbuf]);
+				continue;	// copy out and return
+			}
+		}
+
+		// Out of input, out of decoded output.  Check errors.
+		if d.err != nil {
+			return 0, d.err;
+		}
+		if d.readErr != nil {
+			d.err = d.readErr;
+			return 0, d.err;
+		}
+
+		// Read more data.
+		nn, d.readErr = d.r.Read(d.buf[d.nbuf:len(d.buf)]);
+		d.nbuf += nn;
+	}
+	panic("unreachable");
+}
+
diff --git a/src/pkg/base85/base85_test.go b/src/pkg/base85/base85_test.go
new file mode 100644
index 000000000..01f329830
--- /dev/null
+++ b/src/pkg/base85/base85_test.go
@@ -0,0 +1,193 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base85
+
+import (
+	"bytes";
+	"io";
+	"os";
+	"reflect";
+	"strings";
+	"testing";
+)
+
+type testpair struct {
+	decoded, encoded string;
+}
+
+var pairs = []testpair{
+	// Wikipedia example
+	testpair{
+		"Man is distinguished, not only by his reason, but by this singular passion from "
+		"other animals, which is a lust of the mind, that by a perseverance of delight in "
+		"the continued and indefatigable generation of knowledge, exceeds the short "
+		"vehemence of any carnal pleasure.",
+		"9jqo^BlbD-BleB1DJ+*+F(f,q/0JhKF<GL>Cj@.4Gp$d7F!,L7@<6@)/0JDEF<G%<+EV:2F!,\n"
+		"O<DJ+*.@<*K0@<6L(Df-\\0Ec5e;DffZ(EZee.Bl.9pF\"AGXBPCsi+DGm>@3BB/F*&OCAfu2/AKY\n"
+		"i(DIb:@FD,*)+C]U=@3BN#EcYf8ATD3s@q?d$AftVqCh[NqF<G:8+EV:.+Cf>-FD5W8ARlolDIa\n"
+		"l(DId<j@<?3r@:F%a+D58'ATD4$Bl@l3De:,-DJs`8ARoFb/0JMK@qB4^F!,R<AKZ&-DfTqBG%G\n"
+		">uD.RTpAKYo'+CT/5+Cei#DII?(E,9)oF*2M7/c\n"
+	}
+}
+
+var bigtest = pairs[len(pairs)-1];
+
+func testEqual(t *testing.T, msg string, args ...) bool {
+	v := reflect.NewValue(args).(*reflect.StructValue);
+	v1 := v.Field(v.NumField() - 2);
+	v2 := v.Field(v.NumField() - 1);
+	if v1.Interface() != v2.Interface() {
+		t.Errorf(msg, args);
+		return false;
+	}
+	return true;
+}
+
+func strip85(s string) string {
+	t := make([]byte, len(s));
+	w := 0;
+	for r := 0; r < len(s); r++ {
+		c := s[r];
+		if c > ' ' {
+			t[w] = c;
+			w++;
+		}
+	}
+	return string(t[0:w]);
+}
+
+func TestEncode(t *testing.T) {
+	for _, p := range pairs {
+		buf := make([]byte, MaxEncodedLen(len(p.decoded)));
+		n := Encode(strings.Bytes(p.decoded), buf);
+		buf = buf[0:n];
+		testEqual(t, "Encode(%q) = %q, want %q", p.decoded, strip85(string(buf)), strip85(p.encoded));
+	}
+}
+
+func TestEncoder(t *testing.T) {
+	for _, p := range pairs {
+		bb := &bytes.Buffer{};
+		encoder := NewEncoder(bb);
+		encoder.Write(strings.Bytes(p.decoded));
+		encoder.Close();
+		testEqual(t, "Encode(%q) = %q, want %q", p.decoded, strip85(bb.String()), strip85(p.encoded));
+	}
+}
+
+func TestEncoderBuffering(t *testing.T) {
+	input := strings.Bytes(bigtest.decoded);
+	for bs := 1; bs <= 12; bs++ {
+		bb := &bytes.Buffer{};
+		encoder := NewEncoder(bb);
+		for pos := 0; pos < len(input); pos += bs {
+			end := pos+bs;
+			if end > len(input) {
+				end = len(input);
+			}
+			n, err := encoder.Write(input[pos:end]);
+			testEqual(t, "Write(%q) gave error %v, want %v", input[pos:end], err, os.Error(nil));
+			testEqual(t, "Write(%q) gave length %v, want %v", input[pos:end], n, end-pos);
+		}
+		err := encoder.Close();
+		testEqual(t, "Close gave error %v, want %v", err, os.Error(nil));
+		testEqual(t, "Encoding/%d of %q = %q, want %q", bs, bigtest.decoded, strip85(bb.String()), strip85(bigtest.encoded));
+	}
+}
+
+func TestDecode(t *testing.T) {
+	for _, p := range pairs {
+		dbuf := make([]byte, 4*len(p.encoded));
+		nsrc, ndst, err := Decode(strings.Bytes(p.encoded), dbuf, true);
+		testEqual(t, "Decode(%q) = error %v, want %v", p.encoded, err, os.Error(nil));
+		testEqual(t, "Decode(%q) = nsrc %v, want %v", p.encoded, nsrc, len(p.encoded));
+		testEqual(t, "Decode(%q) = ndst %v, want %v", p.encoded, ndst, len(p.decoded));
+		testEqual(t, "Decode(%q) = %q, want %q", p.encoded, string(dbuf[0:ndst]), p.decoded);
+	}
+}
+
+func TestDecoder(t *testing.T) {
+	for _, p := range pairs {
+		decoder := NewDecoder(bytes.NewBufferString(p.encoded));
+		dbuf, err := io.ReadAll(decoder);
+		if err != nil {
+			t.Fatal("Read failed", err);
+		}
+		testEqual(t, "Read from %q = length %v, want %v", p.encoded, len(dbuf), len(p.decoded));
+		testEqual(t, "Decoding of %q = %q, want %q", p.encoded, string(dbuf), p.decoded);
+		if err != nil {
+			testEqual(t, "Read from %q = %v, want %v", p.encoded, err, os.EOF);
+		}
+	}
+}
+
+func TestDecoderBuffering(t *testing.T) {
+	for bs := 1; bs <= 12; bs++ {
+		decoder := NewDecoder(bytes.NewBufferString(bigtest.encoded));
+		buf := make([]byte, len(bigtest.decoded)+12);
+		var total int;
+		for total = 0; total < len(bigtest.decoded); {
+			n, err := decoder.Read(buf[total : total+bs]);
+			testEqual(t, "Read from %q at pos %d = %d, %v, want _, %v", bigtest.encoded, total, n, err, os.Error(nil));
+			total += n;
+		}
+		testEqual(t, "Decoding/%d of %q = %q, want %q", bs, bigtest.encoded, string(buf[0:total]), bigtest.decoded);
+	}
+}
+
+func TestDecodeCorrupt(t *testing.T) {
+	type corrupt struct {
+		e	string;
+		p	int;
+	}
+	examples := []corrupt{
+		corrupt{"v", 0},
+		corrupt{"!z!!!!!!!!!", 1},
+	};
+
+	for _, e := range examples {
+		dbuf := make([]byte, 4*len(e.e));
+		_, _, err := Decode(strings.Bytes(e.e), dbuf, true);
+		switch err := err.(type) {
+		case CorruptInputError:
+			testEqual(t, "Corruption in %q at offset %v, want %v", e.e, int(err), e.p);
+		default:
+			t.Error("Decoder failed to detect corruption in", e);
+		}
+	}
+}
+
+func TestBig(t *testing.T) {
+	n := 3*1000 + 1;
+	raw := make([]byte, n);
+	const alpha = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+	for i := 0; i < n; i++ {
+		raw[i] = alpha[i%len(alpha)];
+	}
+	encoded := new(bytes.Buffer);
+	w := NewEncoder(encoded);
+	nn, err := w.Write(raw);
+	if nn != n || err != nil {
+		t.Fatalf("Encoder.Write(raw) = %d, %v want %d, nil", nn, err, n);
+	}
+	err = w.Close();
+	if err != nil {
+		t.Fatalf("Encoder.Close() = %v want nil", err);
+	}
+	decoded, err := io.ReadAll(NewDecoder(encoded));
+	if err != nil {
+		t.Fatalf("io.ReadAll(NewDecoder(...)): %v", err);
+	}
+
+	if !bytes.Equal(raw, decoded) {
+		var i int;
+		for i = 0; i < len(decoded) && i < len(raw); i++ {
+			if decoded[i] != raw[i] {
+				break;
+			}
+		}
+		t.Errorf("Decode(Encode(%d-byte string)) failed at offset %d", n, i);
+	}
+}
diff --git a/src/pkg/base85/git.go b/src/pkg/base85/git.go
new file mode 100644
index 000000000..813645e86
--- /dev/null
+++ b/src/pkg/base85/git.go
@@ -0,0 +1,275 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base85
+
+import (
+	"bytes";
+	"io";
+	"os";
+)
+
+const gitEncode = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~"
+
+// The decodings are 1+ the actual value, so that the
+// default zero value can be used to mean "not valid".
+var gitDecode = [256]uint8{
+	'0':	1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
+	'A':	11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
+		24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
+	'a':	37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
+		50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,
+	'!':	63,
+	'#':	64, 65, 66, 67,
+	'(':	68, 69, 70, 71,
+	'-':	72,
+	';':	73,
+	'<':	74, 75, 76, 77,
+	'@':	78,
+	'^':	79, 80, 81,
+	'{':	82, 83, 84, 85
+}
+
+// GitEncode encodes src into GitEncodedLen(len(src))
+// bytes of dst.  As a convenience, it returns the number
+// of bytes written to dst, but this value is always GitEncodedLen(len(src)).
+// GitEncode implements the radix 85 encoding used in the
+// Git version control tool.
+//
+// The encoding splits src into chunks of at most 52 bytes
+// and encodes each chunk on its own line.
+func GitEncode(src, dst []byte) int {
+	ndst := 0;
+	for len(src) > 0 {
+		n := len(src);
+		if n > 52 {
+			n = 52;
+		}
+		if n <= 27 {
+			dst[ndst] = byte('A' + n - 1);
+		} else {
+			dst[ndst] = byte('a' + n - 26 - 1);
+		}
+		ndst++;
+		for i := 0; i < n; i += 4 {
+			var v uint32;
+			for j := 0; j < 4 && i+j < n; j++ {
+				v |= uint32(src[i+j]) << uint(24 - j*8);
+			}
+			for j := 4; j >= 0; j-- {
+				dst[ndst+j] = gitEncode[v%85];
+				v /= 85;
+			}
+			ndst += 5;
+		}
+		dst[ndst] = '\n';
+		ndst++;
+		src = src[n:len(src)];
+	}
+	return ndst;
+}
+
+// GitEncodedLen returns the length of an encoding of n source bytes.
+func GitEncodedLen(n int) int {
+	if n == 0 {
+		return 0;
+	}
+	// 5 bytes per 4 bytes of input, rounded up.
+	// 2 extra bytes for each line of 52 src bytes, rounded up.
+	return (n+3)/4*5 + (n+51)/52*2;
+}
+
+var newline = []byte{'\n'}
+
+// GitDecode decodes src into at most MaxGitDecodedLen(len(src))
+// bytes, returning the actual number of bytes written to dst.
+//
+// If GitDecode encounters invalid input, it returns a CorruptInputError.
+//
+func GitDecode(src, dst []byte) (n int, err os.Error) {
+	ndst := 0;
+	nsrc := 0;
+	for nsrc < len(src) {
+		var l int;
+		switch ch := int(src[nsrc]); {
+		case 'A' <= ch && ch <= 'Z':
+			l = ch - 'A' + 1;
+		case 'a' <= ch && ch <= 'z':
+			l = ch - 'a' + 26 + 1;
+		default:
+			return ndst, CorruptInputError(nsrc);
+		}
+		if nsrc+1+l > len(src) {
+			return ndst, CorruptInputError(nsrc);
+		}
+		el := (l+3)/4*5;	// encoded len
+		if nsrc+1+el+1 > len(src) || src[nsrc+1+el] != '\n' {
+			return ndst, CorruptInputError(nsrc);
+		}
+		line := src[nsrc+1:nsrc+1+el];
+		for i := 0; i < el; i += 5 {
+			var v uint32;
+			for j := 0; j < 5; j++ {
+				ch := gitDecode[line[i+j]];
+				if ch == 0 {
+					return ndst, CorruptInputError(nsrc+1+i+j);
+				}
+				v = v*85 + uint32(ch-1);
+			}
+			for j := 0; j < 4; j++ {
+				dst[ndst] = byte(v>>24);
+				v <<= 8;
+				ndst++;
+			}
+		}
+		// Last fragment may have run too far (but there was room in dst).
+		// Back up.
+		if l%4 != 0 {
+			ndst -= 4 - l%4;
+		}
+		nsrc += 1+el+1;
+	}
+	return ndst, nil;
+}
+
+func MaxGitDecodedLen(n int) int {
+	return n/5*4;
+}
+
+// NewEncoder returns a new Git base85 stream encoder.  Data written to
+// the returned writer will be encoded and then written to w.
+// The Git encoding operates on 52-byte blocks; when finished
+// writing, the caller must Close the returned encoder to flush any
+// partially written blocks.
+func NewGitEncoder(w io.Writer) io.WriteCloser {
+	return &gitEncoder{w: w};
+}
+
+type gitEncoder struct {
+	w io.Writer;
+	err os.Error;
+	buf [52]byte;
+	nbuf int;
+	out [1024]byte;
+	nout int;
+}
+
+func (e *gitEncoder) Write(p []byte) (n int, err os.Error) {
+	if e.err != nil {
+		return 0, e.err;
+	}
+
+	// Leading fringe.
+	if e.nbuf > 0 {
+		var i int;
+		for i = 0; i < len(p) && e.nbuf < 52; i++ {
+			e.buf[e.nbuf] = p[i];
+			e.nbuf++;
+		}
+		n += i;
+		p = p[i:len(p)];
+		if e.nbuf < 52 {
+			return;
+		}
+		nout := GitEncode(&e.buf, &e.out);
+		if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
+			return n, e.err;
+		}
+		e.nbuf = 0;
+	}
+
+	// Large interior chunks.
+	for len(p) >= 52 {
+		nn := len(e.out)/(1+52/4*5+1) * 52;
+		if nn > len(p) {
+			nn = len(p)/52 * 52;
+		}
+		if nn > 0 {
+			nout := GitEncode(p[0:nn], &e.out);
+			if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
+				return n, e.err;
+			}
+		}
+		n += nn;
+		p = p[nn:len(p)];
+	}
+
+	// Trailing fringe.
+	for i := 0; i < len(p); i++ {
+		e.buf[i] = p[i];
+	}
+	e.nbuf = len(p);
+	n += len(p);
+	return;
+}
+
+func (e *gitEncoder) Close() os.Error {
+	// If there's anything left in the buffer, flush it out
+	if e.err == nil && e.nbuf > 0 {
+		nout := GitEncode(e.buf[0:e.nbuf], &e.out);
+		e.nbuf = 0;
+		_, e.err = e.w.Write(e.out[0:nout]);
+	}
+	return e.err;
+}
+
+// NewGitDecoder returns a new Git base85 stream decoder.
+func NewGitDecoder(r io.Reader) io.Reader {
+	return &gitDecoder{r: r};
+}
+
+type gitDecoder struct {
+	r io.Reader;
+	err os.Error;
+	readErr os.Error;
+	buf [1024]byte;
+	nbuf int;
+	out []byte;
+	outbuf [1024]byte;
+	off int64;
+}
+
+func (d *gitDecoder) Read(p []byte) (n int, err os.Error) {
+	if len(p) == 0 {
+		return 0, nil;
+	}
+
+	for {
+		// Copy leftover output from last decode.
+		if len(d.out) > 0 {
+			n = bytes.Copy(p, d.out);
+			d.out = d.out[n:len(d.out)];
+			return;
+		}
+
+		// Out of decoded output.  Check errors.
+		if d.err != nil {
+			return 0, d.err;
+		}
+		if d.readErr != nil {
+			d.err = d.readErr;
+			return 0, d.err;
+		}
+
+		// Read and decode more input.
+		var nn int;
+		nn, d.readErr = d.r.Read(d.buf[d.nbuf:len(d.buf)]);
+		d.nbuf += nn;
+
+		// Send complete lines to GitDecode.
+		nl := bytes.LastIndex(d.buf[0:d.nbuf], newline);
+		if nl < 0 {
+			continue;
+		}
+		nn, d.err = GitDecode(d.buf[0:nl+1], &d.outbuf);
+		if e, ok := d.err.(CorruptInputError); ok {
+			d.err = CorruptInputError(int64(e)+d.off);
+		}
+		d.out = d.outbuf[0:nn];
+		d.nbuf = bytes.Copy(&d.buf, d.buf[nl+1:d.nbuf]);
+		d.off += int64(nl+1);
+	}
+	panic("unreacahable");
+}
+
diff --git a/src/pkg/base85/git_test.go b/src/pkg/base85/git_test.go
new file mode 100644
index 000000000..916859942
--- /dev/null
+++ b/src/pkg/base85/git_test.go
@@ -0,0 +1,183 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base85
+
+import (
+	"bytes";
+	"io";
+	"os";
+	"strings";
+	"testing";
+)
+
+func TestGitTable(t *testing.T) {
+	var saw [256]bool;
+	for i, c := range gitEncode {
+		if gitDecode[c] != uint8(i+1) {
+			t.Errorf("gitDecode['%c'] = %d, want %d", c, gitDecode[c], i+1);
+		}
+		saw[c] = true;
+	}
+	for i, b := range saw {
+		if !b && gitDecode[i] != 0 {
+			t.Errorf("gitDecode[%d] = %d, want 0", i, gitDecode[i]);
+		}
+	}
+}
+
+var gitPairs = []testpair{
+	// Wikipedia example, adapted.
+	testpair{
+		"Man is distinguished, not only by his reason, but by this singular passion from "
+		"other animals, which is a lust of the mind, that by a perseverance of delight in "
+		"the continued and indefatigable generation of knowledge, exceeds the short "
+		"vehemence of any carnal pleasure.",
+
+		"zO<`^zX>%ZCX>)XGZfA9Ab7*B`EFf-gbRchTY<VDJc_3(Mb0BhMVRLV8EFfZabRc4R\n"
+		"zAarPHb0BkRZfA9DVR9gFVRLh7Z*CxFa&K)QZ**v7av))DX>DO_b1WctXlY|;AZc?T\n"
+		"zVIXXEb95kYW*~HEWgu;7Ze%PVbZB98AYyqSVIXj2a&u*NWpZI|V`U(3W*}r`Y-wj`\n"
+		"zbRcPNAarPDAY*TCbZKsNWn>^>Ze$>7Ze(R<VRUI{VPb4$AZKN6WpZJ3X>V>IZ)PBC\n"
+		"zZf|#NWn^b%EFfigV`XJzb0BnRWgv5CZ*p`Xc4cT~ZDnp_Wgu^6AYpEKAY);2ZeeU7\n"
+		"IaBO8^b9HiME&u=k\n"
+	}
+}
+
+var gitBigtest = gitPairs[len(gitPairs)-1];
+
+func TestGitEncode(t *testing.T) {
+	for _, p := range gitPairs {
+		buf := make([]byte, GitEncodedLen(len(p.decoded)));
+		n := GitEncode(strings.Bytes(p.decoded), buf);
+		if n != len(buf) {
+			t.Errorf("GitEncodedLen does not agree with GitEncode");
+		}
+		buf = buf[0:n];
+		testEqual(t, "GitEncode(%q) = %q, want %q", p.decoded, string(buf), p.encoded);
+	}
+}
+
+func TestGitEncoder(t *testing.T) {
+	for _, p := range gitPairs {
+		bb := &bytes.Buffer{};
+		encoder := NewGitEncoder(bb);
+		encoder.Write(strings.Bytes(p.decoded));
+		encoder.Close();
+		testEqual(t, "GitEncode(%q) = %q, want %q", p.decoded, bb.String(), p.encoded);
+	}
+}
+
+func TestGitEncoderBuffering(t *testing.T) {
+	input := strings.Bytes(gitBigtest.decoded);
+	for bs := 1; bs <= 12; bs++ {
+		bb := &bytes.Buffer{};
+		encoder := NewGitEncoder(bb);
+		for pos := 0; pos < len(input); pos += bs {
+			end := pos+bs;
+			if end > len(input) {
+				end = len(input);
+			}
+			n, err := encoder.Write(input[pos:end]);
+			testEqual(t, "Write(%q) gave error %v, want %v", input[pos:end], err, os.Error(nil));
+			testEqual(t, "Write(%q) gave length %v, want %v", input[pos:end], n, end-pos);
+		}
+		err := encoder.Close();
+		testEqual(t, "Close gave error %v, want %v", err, os.Error(nil));
+		testEqual(t, "Encoding/%d of %q = %q, want %q", bs, gitBigtest.decoded, bb.String(), gitBigtest.encoded);
+	}
+}
+
+func TestGitDecode(t *testing.T) {
+	for _, p := range gitPairs {
+		dbuf := make([]byte, 4*len(p.encoded));
+		ndst, err := GitDecode(strings.Bytes(p.encoded), dbuf);
+		testEqual(t, "GitDecode(%q) = error %v, want %v", p.encoded, err, os.Error(nil));
+		testEqual(t, "GitDecode(%q) = ndst %v, want %v", p.encoded, ndst, len(p.decoded));
+		testEqual(t, "GitDecode(%q) = %q, want %q", p.encoded, string(dbuf[0:ndst]), p.decoded);
+	}
+}
+
+func TestGitDecoder(t *testing.T) {
+	for _, p := range gitPairs {
+		decoder := NewGitDecoder(bytes.NewBufferString(p.encoded));
+		dbuf, err := io.ReadAll(decoder);
+		if err != nil {
+			t.Fatal("Read failed", err);
+		}
+		testEqual(t, "Read from %q = length %v, want %v", p.encoded, len(dbuf), len(p.decoded));
+		testEqual(t, "Decoding of %q = %q, want %q", p.encoded, string(dbuf), p.decoded);
+		if err != nil {
+			testEqual(t, "Read from %q = %v, want %v", p.encoded, err, os.EOF);
+		}
+	}
+}
+
+func TestGitDecoderBuffering(t *testing.T) {
+	for bs := 1; bs <= 12; bs++ {
+		decoder := NewGitDecoder(bytes.NewBufferString(gitBigtest.encoded));
+		buf := make([]byte, len(gitBigtest.decoded)+12);
+		var total int;
+		for total = 0; total < len(gitBigtest.decoded); {
+			n, err := decoder.Read(buf[total : total+bs]);
+			testEqual(t, "Read from %q at pos %d = %d, %v, want _, %v", gitBigtest.encoded, total, n, err, os.Error(nil));
+			total += n;
+		}
+		testEqual(t, "Decoding/%d of %q = %q, want %q", bs, gitBigtest.encoded, string(buf[0:total]), gitBigtest.decoded);
+	}
+}
+
+func TestGitDecodeCorrupt(t *testing.T) {
+	type corrupt struct {
+		e	string;
+		p	int;
+	}
+	examples := []corrupt{
+		corrupt{"v", 0},
+		corrupt{"!z!!!!!!!!!", 0},
+	};
+
+	for _, e := range examples {
+		dbuf := make([]byte, 2*len(e.e));
+		_, err := GitDecode(strings.Bytes(e.e), dbuf);
+		switch err := err.(type) {
+		case CorruptInputError:
+			testEqual(t, "Corruption in %q at offset %v, want %v", e.e, int(err), e.p);
+		default:
+			t.Error("GitDecoder failed to detect corruption in", e);
+		}
+	}
+}
+
+func TestGitBig(t *testing.T) {
+	n := 3*1000 + 1;
+	raw := make([]byte, n);
+	const alpha = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
+	for i := 0; i < n; i++ {
+		raw[i] = alpha[i%len(alpha)];
+	}
+	encoded := new(bytes.Buffer);
+	w := NewGitEncoder(encoded);
+	nn, err := w.Write(raw);
+	if nn != n || err != nil {
+		t.Fatalf("GitEncoder.Write(raw) = %d, %v want %d, nil", nn, err, n);
+	}
+	err = w.Close();
+	if err != nil {
+		t.Fatalf("GitEncoder.Close() = %v want nil", err);
+	}
+	decoded, err := io.ReadAll(NewGitDecoder(encoded));
+	if err != nil {
+		t.Fatalf("io.ReadAll(NewGitDecoder(...)): %v", err);
+	}
+
+	if !bytes.Equal(raw, decoded) {
+		var i int;
+		for i = 0; i < len(decoded) && i < len(raw); i++ {
+			if decoded[i] != raw[i] {
+				break;
+			}
+		}
+		t.Errorf("GitDecode(GitEncode(%d-byte string)) failed at offset %d", n, i);
+	}
+}